1. Field of Invention
The present invention relates to a transistor and an electronic device.
2. Description of Related Art
A hetero-bipolar transistor (HBT), which is a device capable of amplifying a high-frequency signal on the order of Gigahertz, has a construction in which a collector layer, a base layer, and an emitter layer are layered in sequence on a semi-insulating semiconductor substrate. When the shape of this hetero-bipolar transistor (unit element) is increased, the output increases, but performance, such as operating speed, decreases. Therefore, usually, in order to form an amplification circuit capable of high speed and a large output, a plurality of hetero-bipolar transistors (unit elements) are formed on a substrate, and the plurality of the unit elements are connected in parallel, forming one amplification circuit as a whole. See, for example, Japanese Unexamined Patent Application Publication No. 6-326330.
However, since the hetero-bipolar transistor is a three-terminal device, if, by using wiring, attempts are made to connect in parallel terminals of a plurality of unit elements provided on the top surface of a substrate, a three-dimensional intersection occurs in the wiring in the conventional case. Since the intersection of this wiring act as a capacitance, which causes the characteristics to be deteriorated, complicated manufacturing measures, such as making the intersection by providing an air gap (air bridge), are necessary.
In order to avoid this situation, there is a method in which collector layers in all the unit elements are made continuous, and a common collector electrode is provided at only one place. However, in this method, since the resistance of the collector layers cannot be decreased sufficiently, it is difficult to realize a high-performance hetero-bipolar transistor.